Automatic climate control is increasingly prevalent in vehicles today. In some vehicles, a driver merely chooses a temperature setting, and a control system operates a climate control system to achieve the desired temperature. The climate control system may control the functions of a fan—e.g., on/off and fan speed—and an air conditioning system. Such a climate control system may also control the position and movement of various air dampers, or air flow doors, to control movement of air through an evaporator core or a heater core, the recirculation of air through the vehicle, the intake of fresh air, or some combination thereof.
Some automatic climate control systems monitor a temperature and humidity level of the vehicle cabin to determine if a defogging operation of the windshield is desirable. When it is determined that an automatic defogging operation is desired, the air conditioning system is typically operated to provide a supply of relatively dry air to the windshield to quickly effect the defogging operation. One limitation of such systems is that operation of the air conditioning compressor uses a relatively large amount of energy.
In the case of a conventional vehicle, where the compressor is mechanically driven by the engine, the increased load on the engine reduces efficiency and increases fuel consumption. In the case of a hybrid electric vehicle (HEV), operation of the compressor often necessitates starting the engine to ensure that the battery is not over-discharged. One of the benefits of an HEV is the fuel savings achieved by driving the vehicle using electric motor power, while maximizing the time the engine is shut down. Thus, automatic defog operations can offset some of the benefits gained by driving an HEV.
Another limitation of conventional automatic defogging systems is that passenger comfort may suffer as the climate control system is operated counter to the wishes of the vehicle occupants. Conversely, if the vehicle occupants are allowed to completely override the automatic defogging operation, the windshield may not clear as quickly as desired. Thus, a need exists for a system and method for vehicle climate control that strike a balance between meeting the comfort requirements of the vehicle occupants, and quickly and efficiently defogging a windshield to provide a clear view for the driver.